1. Field of the Invention
The present invention relates to an azo dye having a novel nitrogen-containing heterocyclic structure, a colored curable composition adapted for forming a color filter for use in a liquid crystal display or a solid state image pickup element, a color filter utilizing such colored curable composition and a producing method therefor, and more particularly to an azo dye having a novel nitrogen-containing heterocyclic structure, a colored curable composition including a nitrogen-containing heterocyclic azo dye, and a color filter and a producing method therefor.
2. Description of the Related Art
Azo dyes, showing optical absorption in various visible regions, have been utilized in various fields as dyes. Azo dyes have recently been utilized in various fields, such as a colorant for synthetic resin, a printing ink, a dye for a sublimation-type heat transfer material, an ink jet ink, a dye for a color filter and the like. One of the major performances required for an azo dye is an absorption spectrum. A color of a dye gives a significant influence on the hue, touch or the like of an article colored with such dye, and provides an important visual effect. For this reason, the absorption spectra of dyes have been investigated for many years. Absorption spectra of azo dyes are reported in various summaries and books, and are detailedly described in the chapters for azo dyes or azo pigments, for example in J. Fabian and H. Hartmann “Light Absorption of Organic Colorants” (Springer-Verlag, Berline, 1980), Heinrich Zollinger “Color Chemistry” (Weinheim, New York, Basel, Cambridge) and Hiroshi Noguchi “Gosei Senryo” (Sankyo Shuppan, 1970).
As a result of recent increases in color images in image recording materials, applications of dyes are becoming more diversified. More specifically, azo dyes are frequently employed for example in a recording material for ink jet recording, a recording material of thermal transfer type, an electrophotographic recording material, a transfer-type silver halide photosensitive material, and a printing ink. The azo dye is also utilized for hair dyeing.
On the other hand, color filters are utilized for recording or reproducing a color image, for example in an image pickup element such as a CCD for use in an image pickup equipment, and in displays such as an LCD or a PDP, and azo dyes are utilized also in such color filters.
In such color image recording material or color filters, there are employed colorants (dyes or pigments) of three primary colors in an additive or subtractive color mixing method, in order to reproduce or record a full-color image. At present, however, there are no colorants having absorption characteristics capable of realizing a preferred color reproduction range, also capable of withstanding various conditions of use and environmental conditions and having satisfactory color hues and satisfactory resistances, and improvements are therefore being strongly desired.
On the other hand, in the color filters, it is already known to use a yellow dye in a green or red filter array as described in Japanese Patent Application Laid-Open (JP-A) Nos. 55-161856 and 6-145543. However, a pyridone azo dye which has been employed as such yellow dye is insufficient in fading stability such as heat resistance and light resistance, and a further improvement is therefore desired. Similarly in a color filter constituted of a yellow filter layer, a magenta filter layer and a cyan filter layer, a further improvement in the fading stability is desired in a yellow dye employed in the yellow filter layer.
Furthermore, the colorants to be employed in these applications are required, commonly, to have absorption characteristics preferable for the color reproduction, a sufficient fading stability under the environmental condition of use and a large molar absorption coefficient.
However, prior azo dyes having a nitrogen-containing 5-membered ring as an azo component, disclosed for example in JP-A Nos. 7-224230, 9-234964, 9-277703 and 2003-246942 are not satisfactory in the color hue, the fading stability and the molar absorption coefficient. Also a method for synthesizing a 5-membered heterocyclic azo dye is disclosed in Journal of Heterocyclic Chemistry, Vol. 22, pp. 813-816(1985) but does not provide an azo dye satisfactory in the color hue and the spectral absorption coefficient.
On the other hand, as a color filter to be formed on a device for realizing a color structure in a solid state image pickup element or a liquid crystal display element, there is known a color filter in which different layers of the color filter are formed in a mutually adjacent manner in a same plane on a substrate. As examples of such color filter, there are known a color filter constituted of a yellow filter layer, a magenta filter layer and a cyan filter layer, and a color filter constituted of a red filter layer, a green filter layer and a blue filter layer, in which such filter layers are formed in a striped pattern or in a mosaic pattern.
For producing such color filter, there have been proposed various producing methods. Among these, so-called color resist method is widely practiced, in which a patterning step of exposing and developing a dye-containing photosensitive resinous composition is repeated by a necessary number of times.
Such color resist method prepares a color filter in a photolithographic process utilizing colored radiation-sensitive compositions in which pigments are dispersed in various photosensitive compositions, and is considered suitable for preparing a color filter for a color display of a large size or a high definition, since it can provide high resistances to light and heat because of the use of pigments and it can provide a sufficient positional precision by a photolithographic patterning.
In case of preparing a color filter by the pigment dispersion method utilizing a pigment dispersion, a radiation-sensitive composition is coated on a glass substrate by a spin coater or a roll coater to obtain a coated film, which is pattern exposed and developed to obtain colored pixels, and the color filter is obtained by repeating such operation for a desired number of colors. Within such pigment dispersion method, a negative-type photosensitive composition utilizing a photopolymerizable monomer and a photopolymerization initiator in combination with an alkali-soluble resin is disclosed for example in JP-A Nos. 1-102469, 1-152499, 2-181704, 2-199403, 4-76062, 5-273411, 6-184482, 7-140654 and 2002-14223.
However, a higher definition is recently desired for the color filter for use in the solid state image pickup element. The prior pigment dispersion system as described above is incapable of improving the resolution, also is associated with a drawback of causing an unevenness in color due to the presence of coarse pigment particles, and is therefore unsuitable for an application requiring a fine pattern such as a solid state image pickup element.
In consideration of such situation, it is already proposed to use a dye for example in JP-A Nos. 6-75375 and 2002-14221. Also a positive-type photosensitive composition is proposed for example in JP-B No. 7-111485 and JP-A No. 2002-14223. However, a dye containing curable composition has been associated with following drawbacks and further improvements have been desired:
(1) A dye is generally inferior in heat resistance and light resistance to a pigment, and is thus unsatisfactory in the fading resistance;
(2) In case a dye has a low molar absorption coefficient, it is required to add the dye in a large amount, whereby other components in the curable composition, such as a polymerizable compound, a binder and a photopolymerization initiator, have to be decreased in relative manner, thereby eventually resulting in deteriorations in a curing property of the composition at the curing, a heat resistance of a cured portion of the composition or a developability of an uncured portion; and
(3) A dye often shows an interaction with other components in the curable composition, whereby it is difficult to regulate the developability (solubility) of a cured portion and an uncured portion.
Thus, the dyes that have been employed in the photosensitive composition are not satisfactory in the fading stability, and, having a low solubility in the photosensitive composition, may show a precipitation in a liquid state or in a coated film and cannot be easily contained at a high concentration.
On the other hand, in the color filters, it is already known to use a yellow dye and a magenta dye in a red filter array as described in JP-A No. 2002-14220. However, a pyrazolone azo dye and a xanthene dye which have been employed for this purpose are insufficient in heat resistance and light resistance. Similarly in a color filter constituted of a yellow filter layer, a magenta filter layer and a cyan filter layer, a further improvement in the fading stability is desired similarly.